Peristaltic Motion in Structurally Adaptive Molecular Crystals Enables Selective Propyne Capture

Published

September 19, 2025

Author(s)

Yun Lin, Hayden Evans, Asif Raza, Sousa Nikkah, Xia Li, Michael Zaworotko, Matthias Vandichel, Soumya Mukherjee, Ognjen Miljanic

Abstract

Cyclotetrabenzoin and its tetraacetate, two macrocyclic porous molecular crystals, were examined as adsorbents for light hydrocarbons, with a particular focus on C3 hydrocarbons: propane, propene, and propyne. While both materials exhibit a preference for propyne, only the tetraacetate—owing to its higher surface area (570 m2 g–1 vs. 42 m2 g–1), enhanced uptake capacity (1.99 mmol g–1 vs. 1.19 mmol g–1) and faster kinetics—achieves dynamic binary separation of propyne from propylene under ambient conditions and various influent ratios (1/1, 1/2, and 2/1, v/v). The high propyne selectivity and separation trends were explained using a combination of in situ synchrotron powder X-ray diffraction and molecular dynamics. Jointly, these techniques suggested that the more rigid, extensively hydrogen bonded structure of cyclotetrabenzoin transports propyne chiefly through pore enlargement. In the case of cyclotetrabenzoin acetate, the absence of hydrogen bonding and larger void volume (25.9% vs. 9.6% in cyclotetrabenzoin) allow extensive structural adaptation that facilitates the capture and transport of propyne through the crystal. On a molecular level, rotation of cyclotetrabenzoin acetate's benzene aromatic panels by ≈19 ° allows adjustment to the propyne structure, maximizing interactions with the C≡C triple bond and the acetylenic hydrogen. Beyond the molecule, extensive fluxionality allows for peristaltic transport of guests through the material, but can also result in transient closure of one-dimensional channels observed in the single-crystal X-ray structure. These results highlight the importance of often subtle structural adaptations in sorbent structures to the bulk separation performance and offer a new design strategy for gas sorption in transiently porous and ultramicroporous molecules.

Citation

Journal of the American Chemical Society

Pub Type

Journals

Keywords

hydrocarbon separation

Citation

Lin, Y. , Evans, H. , Raza, A. , Nikkah, S. , Li, X. , Zaworotko, M. , Vandichel, M. , Mukherjee, S. and Miljanic, O. (2025), Peristaltic Motion in Structurally Adaptive Molecular Crystals Enables Selective Propyne Capture, Journal of the American Chemical Society (Accessed January 8, 2026)